Many herbicides injure crop plants at herbicide application rates necessary to control weed growth. Accordingly, many herbicides cannot be used for controlling weeds in the presence of certain crops. Uncontrolled weed growth, however, results in lower crop yield and reduced crop quality inasmuch as weeds compete with crops for light, water and soil nutrients. Reduction of herbicidal injury to crops without an unacceptable corresponding reduction of herbicidal action on the weeds can be accomplished by use of crop protectants known as herbicide "antidotes" or "safeners".
There are described in the literature various dihaloacyl oxazolidinyl and thiazolidinyl compounds containing a variety of substitutions on the oxazolidinyl or thiazolidinyl moiety, which compounds are known as antidotes, or safeners, for various herbicidal compounds in various crops. For example, a number of patents describe such dihaloacyl oxazolidinyl compounds having as substituents on the oxazolidinyl ring hydrogen, alkyl, cycloalkyl, spirocycloalkyl, alkoxyalkyl, alkanol, heterocycyl, aryl or aryloxyalkyl moieties, which compounds are used as antidotes for herbicides such as .alpha.-haloacetanilides or thiocarbamates in various crops. Typical of such patents are U.S. Pat. Nos. 3,959,304, 3,989,503, 4,072,688, 4,137,070, 4,124,372, 4,186,130, 4,197,110, 4,249,932, 4,256,481, 4,618,361 and 4,708,735 and EP Nos. 0054278, 0,147,365, 190,105 and 0,234,036.
None of the above patents or any other known to the inventors herein disclose any dihaloacyl oxazolidinyl or thiazolidinyl compounds directly substituted with a heterocyclic radical in the 5-position. The above EP 190,105 disclosed one dichloroacetyl oxazolidine compound having a furyl radical in the 2-position; that compound is not within the generic scope of the defined dichloroacetyl oxazolidine antidotes in that patent. The EP 0,234,036 discloses a great variety of dichloroacetic acid amide derivatives including various heterocyclic radicals such as 1, 3-oxazolidines which may be further substituted in non-designated positions with any of a plurality of radicals including the pyridyl and piperidinyl radicals, but the patent fails to exemplify any such compounds.
An effective herbicide must provide a relatively high level of control of grassy or broad-leaf weeds, or both, in the presence of crops in addition to meeting several other criteria. For example, the herbicide should possess relatively high unit activity so that lower rates of herbicide application are feasible. Lower application rates are desirable in order to minimize exposure of the environment to the herbicide. At the same time, such herbicide must be selective in herbicidal effect so as not to injure the crops. Herbicidal selectivity can be enhanced by use of an appropriate antidote in combination with the herbicide. But identification of an antidote which safens a herbicide in crops is a highly complicated task. Whether a compound or class of compounds provides efficacious antidote or safening activity is not a theoretical determination but must be done empirically. Safening activity is determined empirically by observing the complex inter-action of several biological and chemical factors, namely: the type of herbicide compound; the type of weed to be controlled; the type of crop to be protected from weed competition and herbicidal injury; and the antidote compound itself. Moreover, the herbicide and antidote must each possess chemical and physical properties enabling preparation of a stable formulation which is environmentally safe and easy to apply to the field.